The invention relates to a lighting device comprising a light source and units for changing the illumination region, which have two arrangements of transparent plate-type components having parallel elongate imaging elements which are arranged alongside one another and which have a surface deviating from a plane at least on one side, wherein the imaging properties of the component arrangements are changeable and the longitudinal axes of one component arrangement are oriented perpendicular to those of the other component arrangements. In particular, the invention relates to a lighting unit for illuminating buildings, places of interest, objects in exhibitions, for stage lighting and the like.
Lighting devices are used not just to illuminate spaces and to bathe them in more or less diffuse light. The lighting devices are often also used to deliberately direct light onto certain objects or in specific directions. In that case, however, often there is a desire to illuminate only a certain region, for example—in the illumination of buildings—only a particular building and not neighboring buildings. In order to prevent the undesirable lateral emergence of light into regions that are not intended to be illuminated, it is known to provide corresponding screens in front of the lighting unit. Said screens screen off the light, but overall mean a loss of light. The light source therefore has to emit more light than if the entire quantity of light could be concentrated onto the desired region.
The use of screens is therefore firstly a source of unnecessarily high power consumption. Another problem regarding the high power consumption and hence undesirable generation of heat is the fact that for the known lighting devices use is normally made of incandescent lamps, fluorescent lamps, mercury vapor lamps and the like, in which a large part of the power supplied is converted into heat.
In one lighting device of the type mentioned in the introduction (U.S. Pat. No. 3,600,063) a laser is used as the light source. The laser light is expanded in a beam expander in order to enable large-area illumination. Owing to the low efficiency of lasers this is, of course, even less economical than the use of the above-mentioned incandescent lamps, fluorescent lamps or mercury vapor lamps.
The invention addresses the problem of providing a lighting device of the type mentioned in the introduction which can be used to illuminate objects in a targeted manner and with a low power consumption.